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BIO CH 20 - Genes Within Populations Chapter 20 1 Genetic...

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1 Genes Within Populations Chapter 20
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2 Darwin : Evolution is descent with modification Evolution : changes through time 1. Species accumulate difference 2. Descendants differ from their ancestors 3. New species arise from existing ones Genetic Variation and Evolution
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3 Natural selection: proposed by Darwin as the mechanism of evolution individuals have specific inherited characteristics they produce more surviving offspring the population includes more individuals with these specific characteristics the population evolves and is better adapted to its present environment Natural selection: mechanism of evolutionary change
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4 In Darwin’s theory, mutations of unseen genetic elements are the fundamental causative agent for behavioral and structural phenotypes
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5 Natural selection: mechanism of evolutionary change Inheritance of acquired characteristics: Proposed by Jean-Baptiste Lamarck Individuals passed on physical and behavioral changes to their offspring Variation by experience …not genetic Darwin’s natural selection: variation a result of preexisting genetic differences
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6 Lamarck’s theory of how giraffes’ long necks evolved... Behaviors replace mutation as the fundamental causative agent for specific inherited phenotypic traits...does not create a compelling consistent account of the phenotypes seen in offspring...BUT consider epigenetics
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7 Measuring levels of genetic variation blood groups enzymes Enzyme polymorphism A locus with more variation than can be explained by mutation is termed polymorphic. (other forces are at work) Natural populations tend to have more polymorphic loci than can be accounted for by mutation. DNA sequence polymorphism Gene Variation in Nature
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8 Godfrey H. Hardy : English mathematician Wilhelm Weinberg : German physician Concluded that : The original proportions of the genotypes in a population will remain constant from generation to generation as long as five assumptions are met Hardy-Weinberg Principle
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9 Five assumptions : 1. No mutation takes place 2. No genes are transferred to or from other sources 3. Random mating is occurring 4. The population size is very large 5. No selection occurs Hardy-Weinberg Principle
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10 Calculate genotype frequencies with a binomial expansion ( p+q ) 2 = p 2 + 2pq + q 2 = 1
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